The invention relates to the mounting of a worm in a steering gear and to a corresponding steering gear and a power steering system equipped therewith according to the preamble of one of the independent claims.
The invention relates in particular to the mounting of a worm by means of a floating bearing and a fixed bearing, wherein the fixed bearing is designed as a pivot bearing and a spring load is provided to the worm.
A mounting of the type mentioned above is known from DE 101 61 715 A1. There, a first bearing (fixed bearing) is provided at the shaft end of the worm which is connected to the drive shaft of a servo motor (electric motor), the bearing being in turn again pivotably mounted and thus designed in the manner of a pivot bearing. A second bearing (floating bearing) is provided at the other, free shaft end of the worm. The worm is thus radially secured, yet is able to expand in the axial direction and can always securely mesh with a worm gear as a result of the pivot bearing. The pivot bearing thus makes it possible for the worm to be mounted so as to be easily pivoted in the meshing direction toward the worm gear. FIG. 1 shows this known design, which is to say a steering gear 1 designed as a worm gear mechanism. For this purpose, the worm 3 and a worm gear 4 are disposed in the housing 2, wherein the worm meshes with the worm gear and is connected by means of a coupling 8 to the drive shaft 9 of an electric drive motor 10 which is mounted in a bearing 11. The worm shaft as such is mounted in a shaft mounting 5, which comprises a ball bearing 6 in the form of a four-point bearing and is designed as a swivel or pivot bearing. So as to keep the toothing play between the worm 3 and worm gear 4 constant to as great an extent as possible during the entire service life of the gear system, a preloading force is applied radially to the worm 3 and the worm is permanently pressed against the toothing of the worm gear 4 or worm wheel. This is done by means of a preloading device comprising a preloading spring 13 and a pressure device 12. The pressure device 12 can be provided, for example, with a hydraulic device 14 and a pressure piece 15 actuated thereby, the pressure piece directly acting on the bearing 16 or the worm 3. While the wear developing over the service life can thus be automatically compensated for, it has been shown that noise may also occur on the shaft bearing 5, which can be eliminated through the use of an expensive specialty bearing only conditionally.
Other shaft mountings, notably fixed bearings, comprising ball bearings are also known, in which the outer ring of the ball bearing is received in a sliding bearing, or in which the inner ring of the ball bearing is received in what is known as silent bushings, whereby the shaft is likewise pivotably mounted. However, these solutions are complex to implement and have relatively large play, which in turn results in the development of noise, notably during load changes (alternating steering). Moreover, these shaft mountings are susceptible to temperature fluctuations and the service life thereof is not very long.